On-grid domestic battery storage

zeupater

1961Nick wrote: »

I'm confused.:huh:

I'd always thought that a "space heater" was a heater where the source of the heat was within the heater.....as against central heating where the source of the heat is elsewhere.

Is that wrong?

Hi

I can't remember using the term 'space heater' in the recent discussion (although it would be technically correct for a single stand alone unit!), but regularly use the term 'space heating' to refer to heating the space that you live in, or any other enclosed volume that would normally require heat - additionally, DHW means just that: 'Domestic Hot Water' ... how you heat each isn't an issue ... coal, biomass, oil, gas, solar thermal, electrical resistance, wind turbine or anything else makes no difference ... it's simply the provision of heat for comfort or convenience ...

I would have thought that it was pretty self-evident, but there's probably plenty of definitions available to reference if anyone needs to be reassured ...

HTH
Z

joefizz

mmmmikey wrote: »

That's good to hear, and I'll take it as an invitation to be quite frank in sharing my views on some of the points you've made

It's interesting to read what you've said but that certainly doesn't mean I agree with a lot of it. Forgive me for being quite so blunt but to my way of thinking your reasoning and logic borders on stark raving bonkers, particularly in the context of green and ethical moneysaving

1. Moneysaving. As I understand it you've realised that having batteries alongside solar panels gives you access to an abundance of free power in the summer. On the back of this you've splashed out (pun 1 ) on a hot tub, electric barbecue, etc. spending £1000s you hadn't planned to.

Ha ha, yes really, ok I take your point on that one so some clarification. 220 quid inflatable hot tub from asda with quidco originally referenced from this site ;-) When building my garage I took down the old fence and lean to and built a hot tub surround with it and other recycled materials from the garden. We dont pay for water here in NI but I have two 200l water butts so use those as the base (they tend to refill quite quickly where I live).
I havent bought an electric bbq, as I mentioned it seemed a complete waste of money. I do have a gas bbq I can retrofit with a couple of electric heating elements (cost about 40 quid to me which is less than the next calor gas refill).
So yeah, sorry, not exactly thousands but I can see where you are coming from. The hot tub is superb I have to say and pretty much free to run in the summer months other than chemicals required to keep it clean. As its inflatable it can go up and down at a couple of days notice and if no sun I have a hot output from the boiler to get it started.

mmmmikey wrote: »

2. Green & Ethical. You appear to have done nothing (or very little) to use the batteries to reduce your carbon footprint in any of this, choosing to fill your boots with expensive toys to soak up excess supply rather than exporting excess energy back to the grid, reducing the need for carbon producing power elsewhere. Great that you've insulated your house, etc. but that's not really anything to do with the batteries which are the subject of this post. This is your choice of course, but hardly green. Or ethical if your investments are partially funded through public investment through FITs or whatever, which are justified on the basis of carbon saving.

Again a bit of clarification, the batteries are part of the process or system which started with redoing the house (went FIRE at 45, got bored, spent 6 months stripping the house down to its shell and redoing as close to passivhaus and canadian leed standard as the external construction would allow).
The results of that were reducing oil intake from over 2000 litres a year to about 1100. In the years since already that has more than carbon offset the extra materials used.
I reduced my electricity usage to less than a third over 10 years but again struggled to do any more as as I mentioned work etc keeps a hard deck on that so solar panels was the next link because most of the work is summerish and that would be a big offset for all of that. I think in the year before the battery my spend on imported electric was 175 quid. Add in the tariff and export and it was a no brainer both from cost and although it would take a couple of years again to offset the carbon involved in making all the solar panels, inverter etc, over its expected lifespan it would be net positive on that front too.
I'll partly agree about not being totally green and allowing everything to export to NIE at 4p a unit so they can sell it to my neighbours at 17p but hey, nobodys perfect...
..however the excess did allow me to reduce carbon footprint in other aways and that increased usage.
So for example I have a couple of vehicles (2 cars, camper, boat etc) and again Im not even going to try and justify those although both cars were bought new (2000 and 2007). One, an old alfa was starting to be beyond economic recovery so bought myself a welder,angle grinder, blah blah blah and a 20 quid sheet of stainless steel and each sunny day a couple of hours over midday for a month cut out and rebuilt the entire floor plan. Its now up and running and Ive plans this summer to do the same with the camper, down to the shell, replace all the panels, redo the interior (cost total about 2 grand in materials) etc etc.

Within that context its full life cycle and without doing maintenance to both cars Id never recover the carbon offset of a new car etc etc given lifecycles.

Id prefer to not have bought the battery but bought an electric vehicle which could be used as a battery but they arent there yet for my requirements.


Going back to the carbon offset bit, before I had the solar panels I was with a supply company who had 100% eco energy but then they got bought out and went the same way as everyone else. Again not a justification but if I could some how store the vast excess I had and use it at night/cloudy days then that would be less carbon (NI has kept dirty power stations on line due to Brexit) after the initial recovery period based on the energy required to manufacture the battery system in the first place.
Then its about managing the excess and the uneven peak of battery usage.


I mentioned the beer making, long story short, got involved in a local craft brewery, went on a start a brewery course, started one. Use the solar energy in summer brew days and aforementioned water. Other than cost of barley, hops, yeast its free beer ;-) So locally produced with pretty much zero carbon footprint compared to bought stuff. Not really an issue for most people unless you have loads of friends who like to bbq/socialise regularly so now none of us pay for beer....



If you are ever in Iceland I recommend visiting the Hellishedi power plant, they do tours and its quite fascinating what they can do as a system. We all know about geothermal but they take the 'waste' hot water, pump it whatever number of kilometers to Reykjavik and use that to power residential heating systems. When the residential heating systems are done with it they pump the 20-30C water out into pipes under the old town streets which keeps them free of frost and snow in winter.
On the other side they pump some of it to a town of greenhouses which use it in CHP as well as underground to heat the soil so they can grow tomatoes etc all year round.
You dont get that sort of joined up system thinking in the UK.
Im trying to think more like that, other than seeing everything as discrete elements, each element is part of a design and a process which moves other things forwards.
As I mentioned Ive only had the batteries since August last year and hadnt expected they would pay for themselves but I saw enough of what I could do with them in the months up to January to see that taking the next step with my final upgrade to 9.6Kw was going to open up more possibilites.
For example the ASHP which could reduce my oil bill and carbon footprint even further. Im not going to eliminate it but certainly after running it for a year in this configuration and if there were a return to a 100% eco energy supplier I would have no qualms about getting a larger system and replacing oil with it (which requires planning permission over here so a non-trivial task). Right now I dont really have much of an option for moving supplier as I use so little of it. Whilst it appears there are 5 energy suppliers in NI, there are really only two, SSE and ESB (Irish electricity company who own PowerNI and Electricity Ireland and subcontract to others) and they now both have records of my usages with the solar and soon the batteries... persona non grata as I will probably just cost them money.


Again granted from reading and some of the flippant comments it doesnt appear to be that way and I will say yes I could just export the lot but wheres the fun in that ;-) Going back to the moneysaving expert bit, used tools off gumtree, recycling old materials etc etc

Hence the mention of the ISO 140001, thats all about from digging the stuff out of the ground to hopefully not burying it there. Ive reduced my household waste so that my bin only gets emptied every 3 months and this year have started to grow some stuff in the garden, again using excess output for grow lamps, mains powered irrigation from water butts etc etc.

All part of planned, implemented, measured and then draw conclusions and start again (hence deciding to double battery and leave it there).
The battery stuff was interesting because of the nature of the modular system. Yes it was cheaper than the tesla etc (read about it all first on here again) but the modular nature of it means with my background if it does fault I can readily fix it so again the carbon offset parts are built as part of the process. Every single part of my system is designed that way so that whilst interdependent are also replaceable/fixable/upgradable. Reduce, reuse, recycle.

mmmmikey wrote: »

3. Technical understanding. I don't doubt your engineering credentials, but it is clear from some of your posts you haven't fully understood some of the points Z has made. For example, you make reference to not having any space heaters but then talk about your oil fired heating and radiators in the next sentence, not having understood that the radiators are a form of space heating. To be fair, you may have made this comment in the heat of the moment (pun 2 ) but the difficulty I have is once I see someone make a mistake as basic as this alarm bells start ringing. None of us are born knowing what space heating is and the fact that you haven't understood this isn't the issue. The concern for me is that speaking confidently about this online in the belief that you do understand it can lead others to take what you say at face value and point them in the wrong direction. That is why I believe the technical challenges you have been subjected to are so important.

I think we might be tying stuff up with kidology and hard engineering technical terms. The space heater point whilst you may consider radiators as space heaters, traditionally they are more what is considered with traditional ashp,economy 7 and plain diesel, gas and petrol blown air systems. My understanding of space heaters is technical and more to do with movement of air (such as the canadian leed model) and generally speaking wouldnt even consider (hence my posts) that oil or gas fired traditional central heating are space heaters because yes whilst they do heat spaces, they dont do it directly (as in air blown etc).
So from a pure engineering technical point of view space heaters are designed to heat specific spaces whereas central heating is just that, central.

mmmmikey wrote: »

Please be assured that none of this is personal, I just have very, very different views to you and believe your post really belongs on a not-green, unethical moneywasting site!

Gulp - did I really just say all that? Enjoy the summer, anyway :):)

None taken, hopefully the clarifications above help move us along (which was the point of my original post). As I mentioned Ive sucked enough of this information out of various sections of this forum which lead to my original post.
I do recommend Dr Tim Morgans excellent surplus energy economics blog as he shares some interesting ideas beyond what most people consider green and ethical as well as putting energy use in a socioeconomic context.
A darker view again is taken by James Howard Kunstler and whilst not quite ready to break out the hand tools just yet, it did spur me to think about fitting out the garage as a workshop for when I finally FIRE (tried at 45 got bored, went back). Using the panels and batteries to drive the tools to facilitate a local repair cafe just in case JHKs predictions come true ;-)
Certainly from my dialogues with energy suppliers, a lot of what Tim Morgan talks about is certainly under consideration (time of use costs, restricted time of use supply, etc) so a battery system in that context is a no brainer if it ever came to pass but as I mentioned in one of my previous posts, lobbying would be at a power company level to have it locally distributed and owned by them rather than residential. (hence the quote about standard 19 inch rack sizes which I found really really intriguing for a not really domestic product).

joefizz

1961Nick wrote: »

I'm confused.:huh:

I'd always thought that a "space heater" was a heater where the source of the heat was within the heater.....as against central heating where the source of the heat is elsewhere.

Is that wrong?

Yes you are quoting the correct engineering definition of a space heater (ive added this in my long reply as well)

joefizz

zeupater wrote: »

DHW means just that: 'Domestic Hot Water' ... how you heat each isn't an issue ... coal, biomass, oil, gas, solar thermal, electrical resistance, wind turbine or anything else makes no difference ... it's simply the provision of heat for comfort or convenience ...
Z

Strictly speaking, technically, it means Direct Hot Water. As in direct and indirect hot water. Direct hot water means water heated by gas/oil direct boiler, electric immersion heaters etc. Indirect hot water is the use of water heat exchanger in a coil suspended in a tank such as ashp, gas, oil, coal central heating.


You can try to say semantics but the entire conversation was about domestic heating and hot water so the terms direct and indirect were the correct technical interpretations. We were talking about domestic hot water so that was a given in context.



It is confusing though, when people talk in depth about technical calculations then revert to non technical terms in a technical discussion...

mmmmikey

joefizz wrote: »

Ha ha, yes really

Phew - thanks, I'm relieved to see that you took my post in the spirit of "pint in hand/you're having a laugh mate" that it was intended Sometimes difficult to convey that in these forums.



I was quite genuine when I said I found your post and Z's responses interesting just as the exchanges between 1961Nick and Z attempting to reconcile theory and data has piqued my interest in this thread again. Don't tell anyone in case they think I'm being extravagant, but your approach has helped me justify getting the air-conditioning for the bedroom that I've been putting off (will post separately for advice on ASHP)


I can understand and sympathise with those who find the nature of the recent exchanges too detailed and/or robust, but I guess although all are welcome (short of sexism, racism, etc.) you can't please everyone. The fact that this thread has been going for so long and there are still regular contributions suggests that I'm not the only one who enjoys the spirited exchanges and detailed analysis. And if anyone participating doesn't enjoy it then why are you participating? (Genuine question, not an attempt to be clever.)



For me, it's a bit like a large social gathering where people are having different conversations. Some people are talking at a level of detail that fascinates them but others find tedious. Some are having lively debates that they are presumably enjoying but look to others like they are about to start fighting; others are locked in quiet, thoughtful debate. You just have to wander round and join the conversation that matches your own interest and style.


Happy to go with the majority on this.....

mmmmikey

Solarchaser wrote: »

I felt I should finally post here after reading these pages for way over a year.

Why? Because of 1961Nick's post.
As in, I couldn't agree more!!

I've often thought I should post my experience about my 4kw fit solar panels fitted 4 years ago, the difference they, and certain behavioural changes have made to my bills.
More recently the installation of an me3000sp and batteries, and even more recently the addition of an electric car, more solar panels and a hybrid inverter, but I have stopped myself from doing do several times, when I see how anyone who posts something different, sees their every word analysed and assassinated or driven into the most minute detail as to declare the person a liar.

There is great information in this thread, but there is also a real failure to accept that not everything is calculatable to the nth degree, especially when its theoretical.

Kev

Thanks Kev, all fair points and I'm sure I'm not the only one who hopes you decide to share your experience with us.


I honestly don't think what you're perceiving as cross-examination / character assination is intended that way. What I think folks here are trying to do is to really understand where batteries fit into the picture, and it's natural that if someone posts something here a bit out of the ordinary or that doesn't stack up with established thinking others will want to ask questions / challenge it in an effort to better understand it. You'll know from your own research as well that there's an awful lot of complete nonsense posted on different forums from time to time - anyone can post anything and it isn't validated until others have questioned, etc. Sure it spills over into frustration from time to time but it's all driven by interest.


So are you pleased with your investments, what's worked for you, what hasn't etc.?

zeupater

joefizz wrote: »

Strictly speaking, technically, it means Direct Hot Water. As in direct and indirect hot water. Direct hot water means water heated by gas/oil direct boiler, electric immersion heaters etc. Indirect hot water is the use of water heat exchanger in a coil suspended in a tank such as ashp, gas, oil, coal central heating.

You can try to say semantics but the entire conversation was about domestic heating and hot water so the terms direct and indirect were the correct technical interpretations. We were talking about domestic hot water so that was a given in context.

It is confusing though, when people talk in depth about technical calculations then revert to non technical terms in a technical discussion...

Hi

You may be correct if you don't consider alternatives, maybe an acronym search would suffice, but may I suggest your assertion is directed towards the market as a whole as the term Domestic Hot Water (DHW) is used on a pretty universal basis, for example, just to save you searching, just 4 random examples ...

Veissmann
W-B
Vaillant
ed-1:v1:en" rel="nofollow">ISO

I'll take their lead if you don't mind ... note that reference to both direct & indirect DHW cylinder versions are referenced in the reading matter and there are pages & pages to look through in those & elsewhere if you're interested! ..

Z

pile-o-stone

I'm not sure whether anyone has posted this already, but in the hope to get this thread back on track.

"Tesla is launching hardware in which adds backup power capabilities to its Powerwall domestic battery storage system for the first time in Europe.

The addition of the new Backup Gateway 2 will make the Powerwall uninterruptable power supply (UPS) enabled, allowing it to provide backup power in the instance of a power outage. The company said today that the hardware is launching initially in the UK, marking the first time Tesla battery systems have had this capability in Europe.

Homes and small businesses with solar installed will benefit the most from Powerwall. A traditional solar system will shut down during an outage to prevent any power from going back into the grid. However, Tesla’s new tech manages the grid connection and allows solar to continue operating during an outage."


https://www.solarpowerportal.co.uk/news/tesla_adds_backup_capability_to_powerwall_for_first_time


Bulk info on the Tesla Power Wall, with nice pictures:
https://cleantechnica.com/2019/01/19/everything-you-need-to-know-about-the-powerwall-2-2019-edition/

All it needs is to have an export limiter built in as well and I'm buying. My DNO is asking me to pay £1500 to upgrade the grid if I want to add any more solar. I'd happily put that towards a battery and more solar instead.

The dream is to add a further 3kw onto a lean-to pergola (semi-transparent solar panels) and another 2kw frame mounted at the back of the veggie patch. With 10.18kw of solar panels and a battery, I'd finally reach my ambition of being off peak time mains electricity (with economy 7 assisting solar in winter).

EDIT: Ohh, I found this in a Tesla PDF - "Non-Export Mode. In some jurisdictions, customers may choose to make both their powerwall and PV inverter non-export in order to go through a simpler interconnection process. Non-export mode limits the export of energy to zero, even if the powerwall is fully charged and there is excess PV energy"

I now need to find out if this non-export is recognised by UK DNOs!!

Solarchaser

mmmmikey wrote: »

Thanks Kev, all fair points and I'm sure I'm not the only one who hopes you decide to share your experience with us.


I honestly don't think what you're perceiving as cross-examination / character assination is intended that way. What I think folks here are trying to do is to really understand where batteries fit into the picture, and it's natural that if someone posts something here a bit out of the ordinary or that doesn't stack up with established thinking others will want to ask questions / challenge it in an effort to better understand it. You'll know from your own research as well that there's an awful lot of complete nonsense posted on different forums from time to time - anyone can post anything and it isn't validated until others have questioned, etc. Sure it spills over into frustration from time to time but it's all driven by interest.


So are you pleased with your investments, what's worked for you, what hasn't etc.?

Hi Mmmmikey, and thanks for your reply.

I think we can both see where the line of robust conversation ends, and petty point scoring starts, and then going to the nth degree of pedantry to try and prove who can wee higher.
If you doubt that, look above.:-(

If the posters involved in the direct debate took the view of "misunderstanding, now corrected, let's move on" the last few pages would have been much more interesting in my opinion.

Not trying to point fingers, I'm sure we have all posted things in the heat of the moment, that when read back, wish we hadn't, and I'm well aware of how hard it is to back away from that position once you have entered into it.

If I had posted about a space heater, to me that's something with a heat source and a fan, blowing hot air into a space..... but even if theres a different meaning, I wouldn't expect this to form the basis of someone trying to prove they know more than me, or prove I knew nothing about anything...

Essentially I'm saying I think both the characters involved, could do with taking a breath and cooling down.

As I said before, I've followed this thread for well over a year, probably over 2 in fact.

As many that have landed here, (or are lurking as I was). I found this thread by searching g**gle for information on solar batteries.

Anyway I will share my experiences and circumstances, as you have suggested, thanks.

I have a young family, and as they get older, my electric consumption increases. (More electronic games, longer showers, less clothes fitting in same size washing machine tumble dryer)
My wife is stay at home and a bit of a clean freak, so the machines are running most days, several times a day.

Previous to solar panels my annual electric was 7000kwh.
4kw of Solar panels were fitted 4.5 years ago to my sse roof and cut that bill to 5000kw, though some of that will be changing bulbs to LED, and white goods to more efficient models, extra loft insulation.
My good lady now sets the machines to start running at 8am in the summer, rather than always in the evening.... but like I said they are on several times a day, so are on in the evening (and at night sometimes) also.
We also have 2x 9.6kw showers which are on 3 times a day each... and usually in the evening.... not the morning as I'd prefer.

So if I ignore the energy saving by more efficient electricals, then the solar panels which generate around 3500kw annually, save me around 2000kw's annually.
It would be real nice to save the entire 3500.

I get the fit from 4 years ago which I think at last count got me around £500 a year, so with savings and payback, I reckon I break even on the panels in around 4 years... 3 years earlier than the salesman said, which is unusual lol.

So after reading this thread for a while I decided I was going to be an early adopter.
I view it as a little project, and so I dont personally need it to make me money, or even really break even, as long as it doesn't lose me a whack of money, I'll still view it positively.

Anyway 7 months ago a sofar me3000sp bobbed up on Ebay in Aberdeen, and I snapped it up for £750.
It had only 1 pylontech battery with it, and some bits missing.
I also needed to run some cat 5 and T&E cables to make it work in the way I wanted, and so in mid October I finally got it wired up.
I noticed pretty quickly that a 2.4kw battery (2kw useable) was pretty much useless, not least as it limits the charge and discharge on the me3000sp to 1.25kw instead of the 3kw it does when 3 or more are fitted.
So after some research I contacted think renewables in keighley and got another 2 pylontech batteries (£1500) bringing me to 6kwh useable, and at the same time bought a growatt sph3600 hybrid inverter with 5kw growatt battery (£2500)... which is actually a 4.8, so 4kw useable, now 10kwh across 2 systems.

I went for the growatt because it supports a remote ct clamp, and the new inverter was to be mounted in my garage, 5m from the house.

I worked out I had enough room on my garage room for 22 panels on an east / west mount (more like nee and sww), some of it is shaded by a telephone pole and some neighbour's in the morning for a short period, and in the evening, the main house shadows the other side of the garage as the sun goes down, so I looked for panels that wouldn't be too affected by shading.
I found rec twin peak have the connections in the middle of the panel, rather than the top like most panels, and the blurb reckons that this helps it cope with shading better as it's like two half panels rather than 1.

I've noticed that in Australia the general advice is to oversize the panels to inverter, and in fact most inverters note a maximum amount of panels they can take.
So the sph3600 can take 6600w of panels, so for the next month or so I scoured the web for cheap rec twin peak 300w panels.
A set came up new on Ebay, and 6600w of panels were delivered in late December.

I looked at the cost of rail systems to mount them, and thought f*ck that.
Garage is felt roofed osb, so I cut some left over decking boards into strips and some aluminium angle off cuts to make my own racking system which cost ~£60 total.
Like I said, it's more of a project.

Anyway, you asked what worked and what didnt.
For me the me3000sp is a very good system, it ramps up to demand (over 200w) really quickly, and the same with charging, if the export is over 200w it ramps the charging very quickly.
In 10 seconds I'd expect to be over 2500w either charging or discharging.
Much quicker than the growatt.
Between 200w and zero the sofar either does nothing, or tries something, but if the wattage changes it then goes for a 60 second *think* .

If I could parallel 3 of them I could almost cover the 9.6kw shower when its running.
But they dont do parallel.

What I would say though, is that induction hobs dont work particularly well with the sofar system because they switch on for 10-15 seconds at a time, the sofar ramps up, then the induction hob switches off, and it starts to ramp down, then the hob comes on etc etc, so you end up importing exporting, importing exporting.

What also seems to work well is the combination of east / west and a separate south array, the east/ west part still producing 2kw (400w east / 1600w west)when the main south facing has shut down, and then even when the west array has all but the last 3 panels shaded, it's still putting out 250w, and the east array is still putting out 150... dont really get why, maybe the same way wall mounted panels still work when sun is high in the sky.

What also doesn't work... or at least not reliably is the growatt, its poor performance is matched only by abysmal service from growatt.
On standby its supposed to draw less than 3w, its actually drawing 30-60w. Growatt answer is that it's in operation mode not standby.... aye!

I'd advise anyone considering batteries as a way of covering peak usage of over 3kw to make sure it's a system capable of paralelling, as otherwise you can end up in a situation where, let's say the shower is on, the growatt puts out 2.2kw, the sofar 3kw.
Then the shower is switched off, the sofar returns to zero in 5-10 seconds, but the growatt takes a further 5-10 seconds out putting to the grid.... the sofar sees this as export, and starts to charge itself.
So you end up with a situation of double round trip losses as the growatt battery charges the sofar batteries.
If you had two systems the same that could talk to each other, then it wouldn't be a problem.

In terms of battery cycles. Though they have been used for 150+ days, the cycle count as of today is 52, as it only counts a complete charge and discharge.

I'm really looking forward to the difference in the summer months, where fingers crossed ill have little to no import.

My hope here was with two 3600 systems I could in theory produce 7mwh a year, and hopefully reduce the electric bill to 1000kwh.
That took a little side step when the wife made me drive her car 100 miles.
I realised it was gonna need me lying under it for several hours to fix the problems with suspension, and exhaust, and decided it was a good time for the move to electric.

For me the move to electric vehicle was the same as the decision to move to batteries, but in reverse.

For batteries, in my opinion, you need to be using a lot of electricity, to benefit from them.
For electric cars, you need to be doing mostly little mileage to make them work.
The wife's longest journey is a 50mile round trip, and the leaf will do 75 miles most days, so it works for us.

Since getting the leaf, we have *paid* to charge it 3 times, the other 30 or so times, it's been *free* with solar.

Jeeze that was a long post, and I've probably missed loads.

zeupater

Solarchaser wrote: »

.... Jeeze that was a long post, and I've probably missed loads.

Hi

Might be a long post, but it's considered & concise .... I'd rather read 100 at that length & quality than even one 5 liner of something that doesn't stand up to a basic sanity test ....

As mentioned numerous times, there's a sweet spot on batteries where the charge rate can absorb the PV output, the capacity is high enough to compensate for 'normal' periods of poor generation whilst not being too large to justify the additional benefit (returns eventually flatline!) and the discharge rate covers the majority of well managed high loads (ie sequential appliance usage where possible), without expecting to cover the highest demand conditions such as cooking Sunday lunch (hob+oven+ ... etc) ... which you seem to have recognised.

The issue that most miss is that the sweet spot changes in line with overall electricity consumption & usage patterns ... this is why it's not unreasonable to suggest or recommend that efficiency improvement measures are considered before configurations are settled & purchase decisions are made ... it doesn't make sense to have to justify decisions after the fact by unnecessarily 'burning' energy as an accounting exercise! ...

I find the information on lags in demand following interesting as it confirms something that was discussed on here some time back regarding 100% of energy being supplied by a battery and achieving zero exports .... also the on the <200W 'decision making', that's a useful observation that seems to confirm something that I pondered some time back related to the management system working on a clamp based sensor as they tend to display this effect at low currents which is probably why most setups I've come across (/seen) use something similar to the SMA energy meter which should be more reliable (/accurate) & react faster ...

Regarding the clamp based export/import monitoring, do you know whether the system measures & compensates for daily grid voltage variance, PF etc, or does it simply take the voltage from a variable within the management system? .... there's lots of potential for import/export performance issues just on this simple point alone!


HTH
Z